Electrical energy generation in industrialized countries like the United States relies on a variety of energy sources that are then converted into electricity, such as fossil, nuclear, solar, wind and hydroelectric. Apart from the concern of the dwindling supply of fossil fuel, one of the great challenges of energy supply chains is balancing supply with demand. Part of the problem is the inability to store electrical energy in an efficient way so that it can be turned on or off to match high or low energy demand. For example, some sources of energy, such as a nuclear plant, cannot easily be switched off and on or in the cases of the renewable resources, such as wind or solar power, are dependent on natural forces beyond our control which may not be productive when needed or become productive when not needed. These factors represent a difficulty in the integration of such renewable sources in the power grid.
Several battery technologies suitable for large-scale applications have been developed to achieve grid-scale integration for intermittent renewable energy sources. Particularly prominent are molten salt electrochemical cells, for example the sodium sulfur battery (or NaS battery) and the Na—NiCl2 battery (or ZEBRA battery). Such cells are based on high temperature electrochemical systems which rely on the use of selective ion-conductive membranes. Beta-alumina solid electrolyte (BASE) is used as a membrane in several types of molten salt electrochemical cells because of its properties as fast ion conductor. Unlike more common forms of alumina, BASE has been characterized as having a layered structure with open galleries separated by pillars. Sodium ions (Na+) migrate through this material readily since the oxide framework provides an ionophilic, non-reducible medium.
However, alumina is brittle and hard to machine into desired shapes. As such, the production of defect-free alumina membranes usually involves the use of complex ceramic fabrication techniques, with a need for high temperature processes and pronounced limitations in shapes attainable in the final product. Complexity in the fabrication process has direct consequences in the cost of the membranes, while limitations with regard to which membrane shapes are attainable affect the applicability and performance of the resulting electrochemical systems. Under such fabrication constraints, the membrane becomes a cost-driving component for the battery and limits the number of possible large-scale applications, as a membrane having a geometry suitable to the application at hand may be too expensive, if not impossible, to manufacture.